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Scientific analysis on boards

Tuesday June 06th 2023

Révéler l'invisible d'un tableau à l'aide de l'imagerie scientifique. L’analyse scientifique des tableaux est indispensable pour dater le support, observer une signature cachée, un repentir ou un dessin préparatoire, et identifier les pigments. Découvrez les différentes méthodes d’imageries utilisées par les laboratoires CIRAM afin de révéler l'invisible de vos tableaux.

ciram imagerie scientifque

Whether for restoration, conservation or authentication, scientific analysis of paintings is an important and unavoidable step.

First and foremost, the different materials of a painting must be considered to deliver a reliable interpretation. Our scientists date the support (canvas, wood, paper, cardboard...), analyze pigments, mineral fillers, binders and varnishes. To achieve this, CIRAM laboratories carry out a complete study of paintings using carbon-14 dating, chemical analysis and scientific imaging techniques.

The different scientific imaging techniques

Scientific imaging techniques provide invaluable information about a painting. They enable the investigation of all the layers of a painting, from the varnish, to the support, via the preparatory drawing, pictorial layers, repentirs, repaints and any restorations. Natural light, ultraviolet, infrared and X-ray radiography, discover the full range of imaging techniques for analyzing paintings.

Visible light imaging

We distinguish three different kinds of visible light examination:

  • Visible light photography: produced under specific conditions, these images correspond to classic photography;
  • Grazing light photography: this type of photography reveals the state of conservation of the work's surface. Our scientists illuminate the work with a focused beam of light forming a 15° angle with its surface. This technique enables us to identify alterations to the paint layer (lifting, blistering, cracking, etc.), deformations of the support (poor tension of the canvas, cracks or joining of the boards) and alterations such as tears, scratches or dents. Grazing light also provides clues to painting techniques and the painter's style.
  • Transmitted light photography: this is observed on the reverse side of canvas or paper paintings. With this method, our scientists apprehend any holes and tears, it also reveals alterations to the pictorial layers.

Ultraviolet (UV) radiation)

Ultraviolet (UV) radiation lies outside the visible spectrum, and is divided into near UV (380nm to 200nm) and extreme UV (200nm to 10nm).

UV imaging enables the surface layer of the painting to be explored. It uses the fluorescence properties of the varnish, which is more or less intense depending on its composition and alteration. Overpainting on varnish or restorations can be easily spotted.

Important: in the absence of varnish, certain natural pigments can emit a colored fluorescence; this fact must be taken into account to avoid distorting interpretation.

Infrared radiation (IR)

Infrared radiation is located between 780nm and 5mm, beyond the visible spectrum, but on the other side of the ultraviolet. CIRAM laboratories use a so-called "warm" light emission that lies in the near infrared. This makes it possible to record the absorption of infrared radiation by the materials making up the pictorial layers.

Thanks to infrared reflectography, our scientists can bring out preparatory drawings, repentirs and repaints. This imaging method provides grayscale snapshots that correspond to varying degrees of interaction with the initial radiation.

X-ray radiography

X-ray radiography captures an image of a painting's internal structure. The X-ray beam is sent onto the painting and the transmitted X-rays are observed as a function of the selective absorption of the material. This absorption is linked to two parameters:

  • The thickness traversed
  • The density of the object's constituent materials.

With this examination, it is possible to identify damage caused by the passage of time, as well as anthropic actions of all kinds from the creation of the work to the present day. It is also possible to identify repaints and repentirs thanks to contrasts in material density.

The equipment used by CIRAM scientists

Visible light imaging was carried out using a 10-megapixel SAMSUNG® EX2F digital camera equipped with a 24-80 mm f/1.4-2.7 lens.

Infrared reflectography imaging is carried out between 900 nm and 1700 nm using an OSIRIS HD Infra Rouge Opus Instruments Ltd® 16-megapixel digital acquisition system. The equipment used for X-ray radiography is portable, comprising a mano-medical HF 1060 high-frequency X-ray generator, a FUJI D EVO II digital acquisition sensor with automatic triggering and Bluetooth transmission (FDR D-EVO, 35 x 43 cm), and a computer for generator control and image processing (OSIRIX software). The acceleration voltages used are 40 kV, 50 kV and 75 kV. Parameters were controlled using Fujifilm® software.

CIRAM, specialists in art analysis

Thanks to state-of-the-art equipment and expert scientists, CIRAM laboratories date and analyze your paintings, sculptures, ethnographic and archaeological objects. Always at your service, our scientists explain the methods, the limits and ensure that the methodology is always in line with your issues.